The present invention relates generally to acousto-optic tunable filters, and more specifically, to non-collinear or transverse type acousto-optic tunable filters.
The tuning range between the drive frequency and the selected wavelength in a conventional transverse acousto-optic tunable filter (AOTF) is limited to considerably less than an octave of wavelength for a frequency variation of one octave. As a consequence, a single AOTF device has a limited tunable spectral range and cannot cover a tunable range of, for example, but not limited to, a spectral range of 400 to 800 nanometers (nm), which includes the entire visible spectrum, or a similar tunable wavelength range at, for example, but not limited to, infrared wavelengths, in one AOTF device without using a frequency range greater than an octave. Further, using a frequency range greater than one octave in a conventional AOTF causes undesired spurious second harmonic responses. Thus, a design providing a tunable spectrum range greater than one octave without undesired harmonic responses typically requires use of multiple conventional AOTF devices, thereby increasing design complexity and requiring, among other things, greater power and physical surface area.
Therefore, it is a general object of the present invention to provide an apparatus and methods which increase the tunable wavelength range of a single AOTF device to greater than one octave without introducing undesired spurious harmonic responses.
A further general object of the present invention is to provide an apparatus and methods which allow a single AOTF device to have a tunable wavelength range comprising the entire visible light spectrum without introducing undesired harmonic responses.
The method for increasing the tunable range of a single acousto-optic tunable filter includes the steps of generating an active steering beam on a piezoelectric transducer and configuring the electrodes of the piezoelectric transducer to reduce the tuning frequency at short wavelengths and increasing the tuning frequency at long wavelengths. The piezoelectric transducer is mounted in relation with an optically transparent crystal at an angle such that the fixed launch angle in combination with the driving frequency provides a greater that one octave spectra to be filtered in a single AOTF.
These as well as other objects are apparent upon inspection of this specification the accompanying drawings.